a lone wolf
A lone wolf is someone who sits around older kids looking like they just failed a test, but they're actually way cooler and just too awkward to hang out with anyone.
He sat in the corner with the older kids and looked like he had no idea what was happening. But he was actually just waiting for the right moment to shine.
She sat with the older kids like she didn't belong. But she was just waiting for the right moment to be cool.
He sat with the older kids looking like he was about to cry. But he was actually just waiting for the right time to be awesome.